Method and apparatus for generating and superheating vapor



Aug. 14, 1962 METHOD AND APPARATUS FOR GENERATING AND SUPERHEATING VAPOR S. S. WALDRON Filed Dec. 2, 1957 STEAM SEPARATOR INVENTOR.

Stoddard S. Waldron ATTORNEY llnited rates 3 649,105 NETHOD AND APPARATUS FOR GENERATING AND SUPERHEATING VAPOR Stoddard S. Waldron, Lynchhnrg, Va., assignor to The Babcock 8: Wilcox Company, New York, N.Y., a corporation of New Jersey Filed Dec. 2, 1957, Ser. No. 700,072 Claims. (Cl. 122-483) The present invention relates in general to the generating and superheating of vapor, and more particularly to the construction and method of generating and superheating vapor within a double tube heat exchanger.

It has been known to use heat exchange apparatus employing double tube systems as vapor generating units. The double tube system comprising an outer tube arranged concentrically about an inner tube to provide an annular flow space therebetween.

In such double tube heat exchange apparatus, used as vapor generating units, a heating fluid and a vaporizable fluid are passed through the unit in indirect heat transfer relationship. One of the fluids is passed through the inner tube of the double tube while the other fluid flows through the unit in contact with the outer tube of the double tubes. A heat transfer medium is often placed within the annular space of the double tube to transfer heat from the heating fluid to the fluid to be vaporized.

Double tube systems in heat exchangers have been used in some cases to avoid violent chemical reactions and in others to prevent tube failure due to corrosion. In certain cases if the heating fluid and the fluid to be vaporized come into direct contact due to leakage a violent chemical reaction results. Therefore, the annular space of the double tube was arranged to separate the heating fluid and the fluid to be vaporized. In this arrangement any leakage was first developed between the medium within the annular space and either the heating fluid or the fluid to be vaporized. Further by providing leak detection means such leakage was discovered before any harmful results occurred. In other instances of double tube use the heating fluid and the fluid to be vaporized do not have compatible corrosive qualities. If both such fluids were in contact with a single tube, one flowing within and the other flowing about the tube corrosion caused by one of the fluids would result in tube failure. In such a case by providing a double tube system the fluids are separated by an annular space. The interposition of the annular space permits selection of tube surfaces which are compatible with the corrosive qualities of the fluids contacting such surfaces.

There have been various systems used to provide the heat transfer medium for the annular space of the double tube heat exchange apparatus. In some cases a quiescent fluid has been used within the annular space while in others a circulating fluid system has been employed. In certain instances the double tube was arranged so that the annular space Was omitted and grooves were provided between the inner and outer tubes to collect and monitor leakage without using a heat transfer medium.

Previously, whenever a circulating fluid was used as the heat transfer medium. the heat absorbed by the circulating fluid, was not put to any use. An example of the prior art is a steam generator employing a double tube within a shell in which the water to be vaporized was contained within the shell disposed about the double tube. The heating medium, a heated liquid metal, was circulated through the inner tube. A heat conducting medium was circulated through the annular space to transfer heat. However, the heat retained within the transfer medium was not converted into any useful work. The purpose of the annular space in that unit was to sepa- Tamales Patented Aug. 14, 1962 1 ice rate the heating fluid from the vaporizing fluid to prevent any violent chemical reaction which would result from a leak of one to the other.

Accordingly, the present invention provides an apparatus and method for generating and superheating vapor in which a heating fluid flows through a heat exchange zone in a confined stream. A second fluid passes through the heat exchange zone in an enclosed spaced relationship from the heating fluid. The heat from the heating fluid vaporizes the second fluid and the vaporized fluid is then passed in a confined stream in interposed and adjoining relationship to the heating fluid and the fluid being vaporized. The vaporized fluid flowing within the heat exchange zone transfers heat from the heating fluid to the fluid to be vaporized while it is superheated for subsequent delivery to a point of use.

Further, in accordance with the arrangement set forth above, the present invention also provides a double tube system arranged within the vapor generating and superheating unit wherein either the heating fluid or the fluid to be vaporized flows through the inner tube of the double tube while the other passes about the outer tube and the vaporized fluid flows through the annular space of the double tube.

In addition the present invention provides for a liquidvapor separator arranged to receive the second fluid after it is vaporized. The separated vapor from the separator is then passed through the heat exchange zone between the heating fluid and the fluid to be vaporized wherein it acts as a heat transfer medium while it is superheated.

Moreover, in addition to the arrangements set forth above the present invention provides for a steam separator to be located either within or without. the vapor generating and superheating unit.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawing and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.

In the drawing is shown a schematic illustration of one apparatus embodying this invention. The vapor generator and superheater 10 of the present invention comprises an elongated pressure vessel 11 of circular crosssection having dished end portions 12, 13. A vaporizable fluid inlet connection 14 and a liquid-vapor outlet connection 15 are provided to the pressure vessel 11.

Heat exchange fluid inlet and outlet nozzles 16, 17 are located exteriorly of and opening into the pressure vessel 11 at the dished end portion 12.. Each nozzle 16, 17 comprises a cylindrical shell 18, 19 having one hemispherically shaped closed end 21}, 21 and one open end 22, 23. The nozzles are attached to the dished end 12 of the pressure vessel 11 at their open ends 22, 23. The nozzles 16, 17 are partitioned into separate inlet spaces 34, 37 and outlet spaces 35, 36 by inner tube sheets 24, 25 and outer tube sheets 26, 27 all integrally attached to the interior of the cylindrical shell.

A U-shaped double tube 30 is disposed within the pressure vessel 11 and is connected at its ends with the nozzles 16, 17. The double tube 30- comprises an outer tube 32 concentrically arranged about an inner tube 31 and forming an annular space 33 therebetween. The outer tube 32 is secured at its ends to the inner tube sheets 24, 25. The annular space 33 connects the inlet and outlet spaces 34, 35 formed by the inner tube sheets 24, 25, the outer tube sheets 26, 27 and the cylindrical shell 18, 19.

' The inner tube 31 passes through the inner tube sheet 24, and the inlet and outlet spaces 34-, 35 and is secured to the outer tube sheet 26, 27. The inner tube 31 is arranged to connect the outlet .and inlet spaces 36, 37 defined by the outer tube sheets 26, 27, the cylindrical shells 13, 19 and the hemispherically shaped closed ends 20, 21.

A conduit 49 connects the outlet 15 of the pressure vessel 11 With a liquid-vapor separator 41. A second conduit 42 is arranged to connect the separator 41 and the space 34. An outlet connection 43 is provided for the outlet space 35. An outlet connection 44- isprovrded for the outlet space 36 and an inlet connection 45 18 provided for the inlet space 37.

In the operation of the vapor generating and superheating unit as illustrated in the drawing a fluid to be vaporized is supplied to the pressure vessel it through the vaporizable fluid inlet 14. A heating fluid is supplied to the inlet space 37 through the inlet connection 45. The heating fluid is passed from the inlet space 37 to the outlet space 36 through the inner tube 31 wherein it gives up heat to vaporize the fluid within the pressure vessel.

The fluid vaporized by the heating fluid then passes from the pressure vessel 11 through the liquidvapor outlet 15 and the conduit 45] to the liquid-vapor separator 4-1. The vapor separated within the liquid-vapor separator it is passed through the conduit 42 to the inlet space 34. The separated vapor then passes from the inlet space 34 to the outlet space 35 through the annular space 33. The separated vapor passes through the annular space 33 in counterflow relationship "with the heating fluid flowing through the inner tube 31. As the separated vapor flows through the annular space 33 it transfers heat from the heating fluid flowing within the inner tube 31 to the fluid to be vaporized within the pressure vessel ill and at the same time it is superheated. The superheated vapor then passes from the outlet space 35 through the outlet connection 43 to a point of use.

The present invention provides a more efficient, economical and simplified arrangement of a vapor generator and superheater employing a double tube system than has been known in the prior art.

In the present invention the annular space of the double tube serves in a dual capacity. First, as in the prior art, it provides the flow space for the heat transfer medium between the heating fluid and the fluid to be vaporized. Secondly, the annular space serves as a superhcater. in the prior art it was necessary to provide a separate superheater and a source of heat therefor both located outside of the vapor generating unit. However, the present invention, by using the annular space as both a flow space for the heat transfer medium and as a superheater, obviates the need for the separate superheatcr and its source of heat.

The present invention further simplifies the prior art by using the fluid vaporized Within the vapor generating unit to replace the separate heat transfer medium. The vapor generated within the unit is passed through the annular space wherein it is also superheated while it serves as the heat transfer medium between the heating fluid and the fluid to be vaporized. Therefore, the present invention dispenses with the need for a separate heat transfer medium and the additional circulating and piping setup that goes with it.

The present invention permits substantial savings in the type of piping used to contain the heat transfer medium. Previously expensive stainless steel was required for the heat transfer medium piping because of its corrosive resistant qualities. However, the corrosive quali ties of steam are negligible and carbon steel can be substituted for the more expensive stainless steel which has been employed for the outer tube of the double tube and for the piping to and from the annular space. Further the use of steam as the heat transfer medium provides for an effective system of leak detection.

The embodiment herein described provides that all of Cir the vapor generated within the pressure vessel be passed through the annular space of the double tube wherein it is superheated. It should also be understood that only a portion of the vapor generated may be passed through the annular space to be superheated. For example, this arrangement could be used where a quantity of saturated steam is needed for heating or for an industrial process in addition to the superheated steam requirements. Further, the embodiment shown provides for a liquid-vapor separator located outside the setting of the vapor gencrating and superheating unit. It should also be understood that the liquid-vapor separator may be located within the setting of the vapor generating and superheating unit. In addition it is contemplated that the present invention may be used as a once-through vapor generator and superheater in which arrangement the liquid-vapor separator would not be required.

While in accordance with the provisions of the statutes 1 have illustrated and described herein the best form of the invention known to me, those skilled in the art will understand that changes may be made without departing from the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

l. A vapor generating and superheating unit comprising a pressure vessel containing a vaporizable fluid, Wall means forming a plurality of separate nozzles opening to and disposed exteriorly of said vessel, partitions dividing each of said nozzles into a heated liquid metal space and a vapor space, an inner tube having a portion thereof located Within said vessel for the flow therethrough of a heated liquid metal and having its ends opening to said heated liquid metal spaces, an outer tube concentrically arranged about said inner tube to form an annular flow space therebetween and having its ends opening to said vapor spaces, said outer tube submerged in said vaporizable fluid throughout its length within said pressure vessel, means for passing fluid vaporized in said vessel to one of said vapor spaces for the flow of vaporized fluid through said outer tube in interposed and separating relationship to transfer heat from the heated liquid metal to the fluid to be vaporized within said vessel while superheating the vaporized fluid for subsequent delivery to a point of use.

2. A vapor generating and superheating unit comprising a pressure vessel containing a vaporizable fluid, wall means forming a plurality of separate nozzles opening to and disposed exteriorly of said vessel, partitions dividing each of said nozzles into a heated liquid metal space and a vapor space, an inner tube having a portion thereof located within said vessel for the flow therethrough of a heated liquid metal and having its ends opening to said heated liquid metal spaces, an outer tube concentrically arranged about said inner tube to form an annular flow space therebetween and having its ends opening to said vapor spaces, said outer tube submerged in said vaporizable fluid throughout its length within said pressure vessel, a liquid-vapor separator in communication with said vessel and arranged to receive a liquid-vapor mixture therefrom, means passing the separated vapor from said separator to one of said vapor spaces for the flow of separated vapor through said outer tube in interposed and separating relationship to transfer heat from the heated liquid metal to the fluid to be vaporized within said vessel While superheating the vapor for subsequent delivery to a point of use.

3. A vapor generating and superheating unit comprising a pressure vessel containing a vaporizable fluid, wall means forming a plurality of separate nozzles opening to and disposed exteriorly of said vessel, each of said nozzles comprising a cylindrical shell having one closed end and partitioned by two transverse tube sheets integrally attached to said shell into a heated liquid metal space and a vapor space, a double tube comprising an inner tube, an outer tube and an annular space therebetween, said double tube arranged within said vessel and having its ends connecting two of said nozzles, said double tube submerged throughout its length in said vaporizable fluid, said outer tube having its ends secured within the inner of said tube sheets and having said annular space opening to and connecting two of said vapor spaces, said inner tube passing through said inner tube sheets and said vapor spaces and having its ends secured within the outer of said tube sheets and opening to and connecting two of said heated liquid metal spaces for the flow there between of the heated liquid metal means for passing fluid vaporized in said vessel to one of said vapor spaces for the flow of vaporized fluid through said outer tube in interposed and separating relationship to transfer heat from the heated liquid metal to the fluid to be vaporized Within said vessel while superheating the vaporized fluid for subsequent delivery to a point of use.

4. A vapor generating and superheating unit comprising a pressure vessel containing a vaporizable fluid, wall means forming a plurality of separate nozzles opening to and disposed exteriorly of said vessel, each of said nozzles comprising a cylindrical shell having one closed end and partitioned by two transverse tube sheets in tegrally attached to said shell into .a heated liquid metal space and a vapor space, a double tube comprising an inner tube, an outer tube and an annular space therebetween, said double tube arranged within said vessel and having its ends connecting two of said nozzles, said double tube submerged throughout its length in said vaporizable fluid, said outer tube having its ends secured within the inner of said tube sheets and having said annular space opening to and connecting two of said vapor spaces, said inner tube passing through said inner tube sheets and said vapor spaces and having its ends secured within the outer of said tube sheets and opening to and connecting two of said heated liquid metal spaces for the flow therebetween of the heated liquid metal, a liquidvapor separator in communication with said vessel and arranged to receive a liquid-vapor mixture therefrom, means for passing the separated vapor from said separator to one of said vapor spaces for the flow through said annular flow space in counterflow relationship with the heated liquid metal to transfer heat from the heated liquid metal to the fluid to be vaporized within said vessel While superheating the vapor for subsequent delivery to a point of use.

5. A vapor generating and superheating unit compris ing a pressure vessel containing a vaporizable fluid, an outer tube arranged Within said pressure vessel and submerged throughout its length therein in said vaporizable fluid, an inner tube arranged Within and spaced from said outer tube throughout its length within said pressure vessel and forming an annular shaped superheating passage therebetween, first tube sheet means arranged in combination with said pressure vessel and having tube seats to receive and hold the ends of said inner tube, second tube sheet means arranged in combination With said pressure vessel having tube seats to receive and hold the ends of said outer tube, means for passing a heated liquid metal through said inner tube, means for passing fluid vaporized by said heated liquid metal through the superheating passage in separating relationship to transfer heat from the liquid metal to the fluid to be vaporized while superheating the vaporized fluid for delivery to a point of use.

References Cited in the file of this patent UNITED STATES PATENTS 1,604,280 Haag Oct. 26, 1926 1,707,453 Winogradow Apr. 2, 1929 1,800,306 Loflier Apr. 14, 1931 2,346,104 Gunter Apr. 4, 1944 2,739,575 Byerly Mar. 27, 1956 FOREIGN PATENTS 748,264 Great Britain Apr. 25, 1956 

